Delivery of certain wavelengths of radiant energy is facilitated by transmission along flexible silica fibers. The energy is dispersed from the emitting end of an optical fiber in a widening cone. The energy intensity is generally symmetric about the central fiber axis (e.g., uniformly distributed in azimuth) at the emitting end. The distribution of emitted energy orthogonal to the azimuth angle is highly non-uniform, with highest intensity at the central axis, rapidly decreasing with increasing divergence angle relative to the central fiber axis, sometimes approximated by a power cosine function of the divergence angle.
Energy beam guiding structures are known that use refractive media (e.g. optical lenses) in combination with movable reflective media (e.g. mirrors) to focus and direct diverging radiant energy disposed around the input beam axis to a target of interest. The optical lenses typically convert (collimate) the dispersing radiant energy to a second beam with the radiant energy directed more parallel to the input beam axis. The second beam's energy is distributed over a cross-sectional area defined on a target surface oriented in a transverse plane intersecting the optical axis of the second beam. The size of the defined area is typically limited by the diameter of the lenses. The movable reflective media are coupled to transporting mechanisms and are positioned to modify the direction of the collimated beam as a function of time, typically in a raster pattern scan mode. The dynamic positioning of the reflective media is generally arranged so that the energy of the second beam, averaged over a multiple number of scan cycles, is distributed as a less intense, more uniform energy intensity distribution over the desired target surface area. In addition, one or more condensing (focusing) lens can be used to focus the collimated beam energy to a fine point at the target's surface. Combinations of mirrors, prisms, and/or lenses are used to achieve both effects. The typical objective of these combined reflective and refractive elements is to modify the beams intensity distribution over the width of a limited transverse area and to move the scan area over a target surface to produce a less intense, more uniform, energy intensity distribution over a larger area.
In previous laser scanning heads, the beam is typically reflected from two raster scanning mirrors movably mounted in a housing where they are disposed with the first mirror intercepting the input beam, reflecting it to the second mirror, which then reflects the beam toward the target. In other previous laser scanning heads, the beam is refracted through moving optical components to direct the beam toward the target.
Laser-based coating removal systems use pulses of light from high power lasers to ablate or vaporize the paint or other coating from a surface. Each pulse removes the coating from a small region, typically 0.1 to 100 square mm. The laser is pointed to a different area after each pulse, where the removal process is repeated until the entire surface is cleaned.
An advantage of lasers for coating removal is that each laser pulse removes a predictable portion of the thickness of the coating, in the small region impacted by the pulse. This opens the possibility of selective stripping where, for example, the topcoat could be removed but not the primer.
There have been previous designs using color as a selection criterion for selective stripping, such as U.S. Pat. Nos. 5,643,476, and 6,288,362, as well as U.S. patent application Ser. No. 10/272,329. These conventional processes utilize a television camera to observe the field being stripped and a computer to analyze the image. The drawback of this approach is the difficulty in maintaining the correspondence between the TV field of view and that of the laser scanner. Any curvature or movement of the surface causes a mismatch between the camera and laser scanning coordinates. This results in a failure to strip desired locations as well as stripping undesired locations.